U.S. eighth-graders have risen in the world when it comes to math and science skills, a new international study finds, but their younger counterparts are having trouble keeping up.

Results of the third Trends in International Mathematics and Science Study released Tuesday show that math and science skills improved sharply from 1995 to 2003, helping eighth-graders climb in the ranks of 22 countries:

• In math, eighth-graders rose from 17th to 12th. Among a larger group of 34 nations that participated only in 2003, they placed 14th.

• In science, they rose from 14th to seventh. Among a larger group of 45 nations that participated only in 2003, they placed ninth.

• Their average score rose 14 points.

For U.S. fourth-graders, however, results were not as good. Though their average math score remained unchanged, since 1995 they dropped from sixth to eighth among 15 nations. In science, their score dropped six points, and their rank among 15 nations dropped from second to fifth.

While noting the eighth-grade gains, National Science Teachers Association executive director Gerald Wheeler says the poor fourth-grade showing "tells us we cannot afford to be complacent."

"The lack of improvement at the elementary level does not surprise us," he says. "We've been hearing from many elementary teachers that they are not teaching science because of the increased emphasis on literacy. Science is essentially being squeezed out of the elementary classroom."

Tom Loveless, the U.S. representative to the Amsterdam-based International Association for the Evaluation of Educational Achievement, which sponsors the study, says the results show that "we have a lot to learn" from high-scoring countries, especially in Asia.

"The one thing that they have is a very coherent curriculum that's very specific," he says. "You know what you're going to learn" year to year.

Loveless, a researcher at the Brookings Institution, also notes that while U.S. eighth-graders' math scores rose 12 points, 10 points of that gain came between 1995 and 1999; eighth-graders have "stalled out" since then.

Also, he says, while fourth-graders' scores dropped from 1995 to 2003, their scores rose sharply in roughly the same period on another test, the National Assessment of Educational Progress, or NAEP. Between 1996 and 2003, NAEP math scores rose 11 points, a gain that educators have celebrated as solid proof that skills are improving.

Loveless says the international study uses more sophisticated problems and, unlike NAEP, doesn't allow calculators on some problems, making it "just plain harder."

"There is no reason why American kids can't do mathematics that other kids around the world are doing," he says. "At fourth grade, math curriculum is pretty standard worldwide."

A study of practical math skills released last week found that U.S. 10th-graders placed 24th out of 29 nations.